In computing, one type of data storage scheme using multiple storage drives to share or replicate data among the storage drive is referred to as a RAID system. The acronym RAID stands for redundant array of inexpensive disks, or redundant array of independent disks. Depending on the configuration of the RAID system, typically referred to as RAID level, the benefit of RAID can include one or more of increased data integrity, fault tolerance, throughput or capacity when compared to a single drive. One of the most popular RAID levels is RAID5. RAID5 has achieved popularity due to its low cost of redundancy. RAID systems can combine multiple low cost older technology devices into an array that offers greater capacity, reliability, speed, or a combination thereof, than is affordably available in a single device using the latest technology.
In a RAID system, a portion of the storage spaces of one or more physical drives (PD) are mapped to a single virtual drive (VD). The VD presents the storage space distributed amongst one or more PDs as a contiguous array of storage space to an operating system. The operating system sees a single VD. An adapter receives Input and output (IO) commands from the operating system and processes the IO commands to read data from or write data to the VD. The adapter further generates specific IO commands to read or write data to specific portions of the PDs so as to complete the IO commands received from the operating system.
In the process of reading or writing data to the PDs, the adapter temporarily stores the data in a memory, sometimes referred to as cache lines. The data stored in the cache lines are manipulated prior to the completion of the IO commands. The manipulation may involve one or more of arithmetic or logical operation on the data stored. As an example, the manipulation may be to validate the data, As yet another example, the manipulation may be to generate error detection or error correction codes. Another use of a cache line can be to accumulate the data from all PDs that is necessary to satisfy the I/O request before beginning transfer to the host.
Existing techniques may not efficiently allocate and use the cache lines, when limited amount of memory is available to be allocated for cache lines.